The invention relates to a process for degassing liquids in closed systems by applying a pressure which is lower compared to the system pressure.
In removing gases from liquids, primarily from water, one generally differentiates between
1. removing (venting) excess gases which exceed the specific solution equilibrium,
2. driving out (degassing) chemically dissolved gases.
1.) Gases comprised in excess in water generally present considerable problems in circulating systems (heating systems, cooling systems, air-conditioning systems). As extremely fine air bubbles, they generate flow noises, cavitation and erosion in the materials and degrade the uniform heat transport in the pipe network and on the surfaces provided for the heat exchange, such as coolers and heating surfaces.
To avoid these problems, ventilation equipment is produced which operates generally with a stop valve disposed in a chamber and connected with a float. When the chamber is filled, the rising float closes the valve. Conversely, the float opens the valve when air enters the chamber. Such ventilation devices are frequently air collection pots, cyclone pots or vessels with massive bodies which are intended for the extremely fine air bubbles to combine into larger ones in order to rise subsequently in the chamber of the ventilator.
2.) If greater gas volumes are comprised in the water than are necessary for chemical saturation, this quantity represents a feeding reservoir to reestablish the natural saturation concentration which is lost, for example, through the reaction of a gas with the materials in the solution. In order to drive out the excess gas and also the gases comprised in the solution, thermal degassing equipment is being manufactured in which, on the one hand, by increasing the temperature, the gas solubility is reduced and, on the other hand, the expulsion effect is enhanced thereby that steam is forced through the water to be degassed and the resulting steam bubbles entrain the gas particles in the water and carry them outside to the outside atmosphere.
Other devices generate a reduced pressure above the level of the liquid whereupon the gases also escape to the surface.
Regarding 1.)
According to Henry""s law, ventilation devices can only remove those quantities of gas which are greater than the factors temperature, pressure and medium properties permit in terms of solubility. In principle, in a circulating system two different pressure regions always obtain between intake and pressure region of a circulation pump such that in theory a ventilator disposed on the intake side of a pump should transport gas out of the system. But in practice, narrow limits are set because the ventilator must be under minimum pressure so that its float chamber remains filled. Otherwise the float drops and opens the ventilation valve such that air can be drawn in via the ventilator (the ventilator becomes an aerator).
But if a minimum pressure is required on the low-pressure side, the air can only be incompletely removed. A further disadvantage of this type of ventilation is that, due to the high flow rate of the water, the microbubbles can only reach the float chamber of the ventilator in small quantities if at all.
Regarding 2.)
According to Henry""s gas law, as expanded by Dalton, the partial pressure acting upon a solution, the temperature and the type of medium determine the solubility of gases. With the known technique of thermal degassing, extremely good results can be attained in this regard. A marked disadvantage of this technique, however, is that it requires large and expensive equipment: a steam generator for producing the expulsion steam and a collecting vessel with degasser device comprising large distributor surfaces on which the water can be exposed to the steam. Part of this equipment includes extensive tubing, regulating elements, control means and the safety technique of steam operation. Such thermal degasser installations are a fixed standard component in steam generation installations.
In closed cooling water circuits, heating or cooling water circulations, they are neither economically nor practically applicable since the degassed water would have to be heated and subsequently cooled again to the circulation temperature.
The problem is similar in so-called fast steam generators in which a relatively small system water quantity is present and for which a thermal degassing installation would be too large.
Required is a cost-effective apparatus for mobile and stationary application, with which excess gas, as well as also the chemically dissolved gases, can be removed from a liquid (for example water). It should not be necessary to raise the temperature of the liquid to be degassed and the apparatus should be operable in a simple manner and require low energy for its operation.
Solution
The task is solved according to the invention thereby that from a water system a portion of the water is extracted and transferred to the degassing container of the described apparatus. By extracting a portion of the liquid and transporting it to a storage container the total pressure (and thus the partial pressures on all gases) is lowered in the degassing container so far that the boiling point of the liquid is exceeded and the liquid boils. The solution equilibrium of the dissolved gases shifts toward the left and as a consequence all excess gases are driven out with the steam bubbles. The temperature of the liquid is not raised.